Investigations will be continued to define the molecular structure of equine herpesvirus (EHV) genomes and to ascertain the relationship between viral gene structure and function. Overall goals concern the elucidation of viral DNA sequences, gene products and alterations in viral gene programming that are involved in mediating oncogenic transformation and persistent infection. Toward these aims, the following studies will be continued: 1) to use restriction enzymes methodologies, electron microscopic techniques and DNA hybridization methods to ascertain the genomic structures of standard EHV-1, EHV-2 (ECMV; cytomegalovirus) and EHV-3 (venereal disease virus) and of EHV-1 defective interfering (DI) particles that establish persistent infections of hamster and mouse cells. 2) to use recombinant DNA technology to generate libraries of EHV DNA fragments for use in experiments such as fine mapping and sequencing defined genomic segments of biological and structural importance, transfection assays to test fragments for transforming potential and capacity to alter viral gene programming, etc., 3) to identify by DNA hybridization methods the DNA sequences shared by these three viruses that differ in biology and to determine whether related DNA sequences are arranged colinearly and whether they mediate similar functions, 4) to examine the regulated programming of EHV gene expression in cytocidal infection and continue to define the properties of alpha, beta and gamma mRNAs and polypeptides, 5) to map polypeptides to specific mRNAs and DNA loci by in vitro translation methods, 6) to elucidate alterations in EHV gene products and/or in gene programming in cells persistently infected with EHV-1 DI particles or ECMV, and in cells harboring defective DNA fragments, 7) to analyze a variety of EHV-1, -2, and -3 transformed and tumor cells in hamster and mouse models for viral DNA sequences so that the nature, arrangement and role (initiation and/or maintenance) of these viral genes in transformation may be elucidated, and 8) to conduct transfection experiments to evaluate whether specific EHV cloned DNA fragments can mediate transformation.